A joint investigation by the United Nations and the global chemical weapons watchdog has established that President Bashar al-Assad's regime and the Islamic State (IS) group have carried out three chemical weapons attacks in Syria.

According to a report seen by the Reuters and AFP news agencies, Syrian government forces are responsible for two toxic gas attacks in Idlib province – in April 2014 and March 2015. Both cases involved the use of chlorine.

The panel also determined there was sufficient information to conclude that IS militants used sulfur mustard gas in Marea, north of Aleppo, in August 2015.

However, the year-long inquiry by the United Nations and Organization for the Prohibition of Chemical Weapons (OPCW), which was authorized by the UN Security Council, was unable to draw any conclusions in the other six cases that it has been investigating.